Self-adjusting electrode support



M y 4 I v c. H. BACHMAN SELF-ADJUSTING ELECTRODE SUPPORT Filed Sept. 27,1944 v Inventor: v Charles H. Bachman,

b9 WW6.

His Attorney.

Patented May 14, 1946 SELF-ADJUSTING ELECTRODE SUPPORT Charles H.Bachman, Scotia, N. Y., assignor to General Electric Company, acorporation of New York Application September 27, 1944, Serial No.556,023 Claime (01. 250-452) The present invention relates to cathoderay tubes and it has for its object to provide an improved electron lenssystem for such a tube.

In a cathode my device, such as an electron microscope in which avisible image is formed by the action of an electron stream, it iscustomary to use an electrostatic lens system in the form of a pluralityof metallic disks axially aligned and spaced the center disk operatingat a different potential from that of. the outer ones. One of theproblems in the construction of an electron lens of thisltype is that ofmaintainingvery accu% rate alignment of the elements and, atrthe sametime, insulating one or more elements from the rest.- 1

It is an object of the present invention to pr vide an improvedinsulator -meansfo r such electrostatic lens systein.

It is .a further object of mylnvention to provide a newand'improvedinsulator for supporting-a removable .electrodein anelectronic tube which permits easy insertion of the electrode in ;theinsulator and which prevents vibration ofthe electrode in its insulatorsupport. I a

The foregoing objects are accomplished in accordance with one embodimentof the invention by providing 'an insulator. in the form of a rod whichextends around substantially the entire periphery of the electrodemember operating at a high potential with respect to an enclosingenvelope and which is grooved at a plurality of points to support theelectrode, Iniaddition, the insulator is slotted in at least onepoint toform a spring-like section which may be deflected. to insert theelectrode in the grooves in the :in-

sulator. I a

The features which I desire to protect herein are pointed out withparticularity in the appende ed claims. The invention itself may best beunderstood by reference tothe following description taken in connectionwith the accompanyin drawing, in which Fig. 1 shows schematically anelectron microscope which includes an electrostatic lens system of thetype considered in the present invention, and Fig. 2 is an enlarged endview of the insulator used in my improved lens system.-

Referring to Fig. 1, there is shown an electron microscope comprising anelongated vacuumtight container I of a tubular metal construction.

At one end of the container there is rovided a glass insulator 2 whichserves to support an electron source in the form of a filamentarycathode 3. Thecathode is surrounded by a tubular metal member 4 whichconfines the emitted electrons to a narrow beam and is cooperativelypositioned with respect to an apertured electrode 5 which is in contactwith the metal envelope 1. The opposite end of the envelope I is sealedby a glass window 6. A fluorescent coating forming a viewing screen I isplaced on the inner surface of the window 6. In the normal use of theapparatus, the envelope I and the apertured electrode 5 are maintainedat ground potential and the cathode is maintained at a high negativepotential, for example, being connected to a potential sourcerepresented by the battery 8 so thatelectrons emitted from the cathodeare projected axially of the container with the object of producing avisible image on the fluorescent screen-I. Between the cathode, 3 andthe image-reproducing screen I there is placed an object 9 supported byany suitable supporting means (not shown) and to be trans-radiated by anelectron beam, the beam being passed through the object and its passageassuming the characteristics of the object. r r In order that theelectron beam, after modification in accordance with the structuralcharacter of the object under investigation as the beam trans-radiatesthat object, may be caused to provide an enlarged visible image of the.object in accordance with the intended use of the micro scope, the beamIll, after passing through the object, is caused to pass throughanelectron lens system of known character. In the drawing, the lens systemis illustrated as of the electrostatic type and comprises a series ofthree apertured metallic diaphragms numbered II-I3 axially aligned andspaced. The diaphragms or disks arev provided, respectively, withcentral apertures I4, I 5, I6 through which is projected the cathode raybeam to be deflected by theelectron. lens system. To this end, the outerdisks I land I3 are connected to the positive terminal of the battery. 8by conductive connection with the inner surface of the tube I, While thecentral disk I2 is connected to the negative terminal of this batterythrough a conductor H which is brought into the microscope enclosure Ithrough an insulating bushing IS. Because of the resultant difference inpotential between the diaphragm I2 and the diaphragms .I I, I3, lensfields. are established be tween these diaphragms which have the effectof refracting the electron beam in a manner analogous to the refractionof a light beam in an optical lens. Additional lens fields may beemployed in an electron microscope where so desired.

The cute-r disks I I, l 3 are machined to fit snu ly within the envelopeI. The center electrode I2 is supported by an insulator I9 to bedescribed Where it is desired to operate the electrode 7 l2 at very highpotential with respect to the remaining part of the electron system, thesurface and volume leakage of the insulating means employed must beconsidered. One manner in which the insulating path may be increased,while the insulating area is reduced, is illustrated in the enlargedview of insulator l9 shown in Fig. 2, in which the rod-like insulator I9is formed of a suitable insulating material, such as porcelain, Micalex,or of a vitreous material, such as Pyrex. The member E 9 extends aboutsubstantially the entire periphery of the len member I2 and is bent intoa shape such that it contacts the envelope l and lens member 2 ataplurality of spaced points 24 on lens l2 and points 25 on envelope I.The portions of the insulator member l9 adjacent the points 24 aregrooved to engage the outer edge of the lens member or electrode [2,while the insulator I9 is machined at the points 25 to conform to theinner diameter of the invelope I.

In manufacturing the insulator, the rod-like member [9 is formed ofaslightly larger outside diameter and a slightly smaller inside diameterthan is normally desired. The insulator may then be held to a face plateusing three holes 26 drilled through the insulator adjacent the points24 a means to support the insulator on such a face plate. The grooves 24are then ground in the insulator and the surfaces 25 are similarlyprepared as by grinding. After the insulator is thu shaped as to innerand outer diameters and as to thickness, it is removed from the faceplate and anarrow blade saw is used to cut slots 21 through the holes 25and parallel to the sides of the insulator. Likewise, a narrow slot 28is cut through one of the contact points 25. Alternatively, the slotsmaybe molded inthe original insulator blank.

In the use of the insulator, the slots 21 provide means for permittingeasy insertion of the lens l2 in the grooves at points 24. The slot 28permits decreasing the outer diameter of the insulator to permit easyinsertion within the envelope I9. During such insertion of the lensstructure in the envelope, arms 29 formed by the slots 27 act as springswhich facilitate insertion of the lens in the envelope.

One of the advantages of my improved insulator is that the spring arms.29 of the insulator take up any wear which would ordinarily causelooseness of the lens electrode. Suchlooseness is obviously undesirable,since it allows vibration of the center electrode of the lens and alsopermit the electrode to locate in off center positions causingaberrations of the lens system. Another advantage is the long length ofthe insulator between the electrode [2 and the envelope I which permitsoperation of the electrode l2 at increased potentials over those whichare normally permitted.

The inventionadescribecl herein a may be used to advantage in cathoderay device orin other types of electronic tubes for supporting anelectrode. Numerous additional modifications may obviously be made to myinvention and I aim in the appended claims to cover all suchmodifications at come within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In an electronic tube having a metallic envelope and a metallicelectrode maintained at a substantial voltage with respect to said en-'velope,,an insulator for supporting said electrode within said envelopecomprising a rod forming a substantially closed loop engaging saidelectrode and said envelope at a plurality of spaced points said rodbeing grooved at its points of engagement with said electrode and havinga longitudinal slot at one of said point to permit insertion of saidelectrode in said grooves.

2. In an electronic tube have a metallic envelope and a metallicelectrode maintained at a substantial voltage with respect to saidenvelope, an insulator for supporting said electrode within saidenvelope having a central aperture for receiving said electrode, saidinsulator having a plurality of flexible arms adjacent said apertureadapted to engage the outer edge of said electrode to prevent vibrationof said electrode.

3. In an electronic tube having a metallic envelope and a metallicelectrode maintained at a substantial voltage with respect to saidenvelope, an insulator interposed between said electrode and saidenvelope, said insulator being grooved at its point of engagement withsaid electrode and being provided with a resilient arm near said pointof engagement to facilitate insertion of said electrode in said grooves.

4. In a cathode ray tube having a metallic envelope and a centrallyapertured metallic disklike lens member maintained at a substantialvoltage with respect to said envelope, an insulator' for supporting saidlens member within said envelope comprising a rod member extendingaround substantially the entire periphery of said lens member andcontacting said envelope and said lens member at a plurality of spacedpoints, said memberbeing grooved at said points and said member having alongitudinal slot to permit flexing of said member and insertion of saidelectrode in'said grooves.

5. A self-adjusting support for an electrode comprising a member havinga central aperture provided with a groove for receiving said electrode,said member being provided with a slot parallel with said groovedportion for increasing the diameter of said aperture to permit insertionof said electrode in said grooves.

CHARLES H. BACI-IMAN.

